The present invention relates to sliding vane rotary paddle pumps, and in particular to a rotary paddle pump having continuous carbon fiber reinforced polyetheretherketone (PEEK) sliding vanes and other parts that provide longer operational life from low wear rates and a low propensity of catastrophic failure due to foreign object impact damage.
Rotary paddle pumps using sliding vanes are in wide application for moving air or other fluid or for evacuating closed vessels. Rotary paddle pumps are, in general, composed of a rotating rotor, sliding vanes, side plates, and a mechanical means to drive the rotating rotor. A circular shroud with an eccentrically displaced rotor or an oval shroud with a centrically placed rotor contains the motion of the sliding vanes. The vanes slide in and out of radial groves which are cut into the rotor along its entire length. Centripetal acceleration during rotation of the rotor forces the vanes into sliding contact with a stationary shroud. The extension and retraction of the vanes against the shroud provides the variation in volume of each chamber of a multi-vaned pump necessary to move air through the device. Side plates then form the complete enclosure of the alternately contracting and expanding volume between paddles. Intake and exhaust ports which deliver and collect air flowing into and out of the working volumes of the pump can be established in the shroud or side plates. During operation of the pump, the vanes slide inwardly and outwardly in the grooves in the rotor and the edges of the vanes are in constant sliding contact with the side plates and shroud. The zero clearance is required to avoid leakage which diminishes the efficiency of the pump.
With zero clearance between rotating and non-rotating components, rotary paddle pumps for moving air require self lubricating materials or air-lubricant separators to avoid contamination of the air stream. An early application of a self lubricating carbon graphite composite material for all parts in sliding contact is disclosed in U.S. Pat. No. 3,191,852 issued to Kaatz et al. The Kaatz design used the carbon graphite composite material for both the vanes and the rotor. These carbon-based parts were primarily made by compressing carbon graphite and various organic binders under high temperature and pressure. Unfortunately, carbon parts made in this manner exhibit poor tensile strength and propensity to fracture and chip which leads to failure of the pump. These failures tend to be catastrophic, especially if foreign objects are ingested. Attempts have been made to minimize the number of carbon parts as disclosed in U.S. Pat. No. 4,804,317 issued to Smart et al. and U.S. Pat. No. 4,198,195 issued to Sakamaki et al. or by replacing the carbon parts with stronger carbon-based parts or other materials coated with a self-lubricating coating. As disclosed in U.S. Pat. No. 4,820,140, Bishop used metallic parts with a self-lubricating lead filled polytetrafluoroethylene (PTFE) coating as side wear plates but not the sliding vanes themselves. The coating prevents oxidation of the stationary components in sliding contact with the vanes and rotor which can lead to pump failure by presenting a roughened surface which can cause fracturing and high wear of the carbon-based material. Later, in U.S. Pat. No. 5,181,844, Bishop et al. disclosed a strengthened carbon vane. The new material was composed of carbon or graphite fibers formed into a cloth weave and held in a densified carbon matrix. Laminates of the carbon/carbon material were used in their preferred embodiment. Further, the carbon vanes were impregnated with a TEFLON based thermoplastic for claimed improved wear resistance. Claimed to be more dependable and consistent in performance, the carbon/carbon composite is still susceptible to chipping and fracture.
In order to address the drawbacks associated with the prior art carbon and carbon/carbon vanes, rotors, and or side plates, the present invention uses continuous carbon fiber reinforced polyetheretherketone for the sliding vanes, and the portion of stationary air transfer side plates in contact with the moving rotor. Polyetheretherketone is an aromatic polymer whose construction consists of ether, ketone, and phenyl groups. Unfilled and unreinforced PEEK has a low coefficient of friction and exhibits self-lubricating character but lacks the strength and rigidity necessary for application to vaned rotary pumps. By reinforcing the PEEK with a carbon-fiber weave, the material becomes very strong and has a low coefficient of thermal expansion while maintaining the required self-lubricating character of the material used in prior art but being more resistant to fracture and chipping. The carbon-fiber reinforced PEEK also maintains these characteristics at very high sliding contact speeds making it suitable for unlubricated operations. Normally fabricated by winding continuous carbon-fiber impregnated with PEEK resin onto a mandril to form circular bearings, the present invention employs carbon-fiber reinforced PEEK which has been laid in flat sheets with varying fiber bias and cured in an autoclave. The thickness is established by combining a plurality of laminated fiber layers and the final shape is then machined to the desired dimension.
While employing a metallic rotor and shroud, the continuous carbon-fiber reinforced PEEK is employed in the sliding vanes. Further, continuous carbon-fiber reinforced PEEK, the preferred embodiment, is utilized in the portion of the stationary components, namely the air transfer side plates, in contact with the metallic rotor. In doing so in the preferred embodiment, a minimum of non-metallic parts are employed. The carbon-fiber reinforced PEEK does not need an additional coating since it does not oxidize and is already self-lubricating. In this embodiment, the invention exhibits characteristics necessary for application in an unlubricated rotary paddle pump, namely, self-lubricating, high flexural and tensile strength, low coefficient of friction, low coefficient of thermal expansion, low wear and nearly complete resistance to chemical attack. It is also possible to form the rotor and the shroud from carbon-fiber reinforced PEEK. Pump parts manufactured from continuous carbon-fiber reinforced PEEK exhibit dependable and consistent performance over a wide range of temperatures and atmospheric conditions.